ISOTERMAS DE ADSORCION PDF

Se determinaron las isotermas de adsorción de humedad en harina de yuca a 20 , 25, 30 y 35ºC mediante el método gravimétrico en el intervalo de actividad de. Download scientific diagram | Isotermas de adsorción-desorción de N 2: a) Al- MCM, b) Mn-Al-MCM, c) Jacobsen quiralAl-MCM from publication. Download scientific diagram | Isotermas de adsorción-desorción de la roca BC-1, mostrando la zona de f ormación de la monocapa (M). from publication.

Author: Dojinn Kasar
Country: Kazakhstan
Language: English (Spanish)
Genre: History
Published (Last): 8 November 2005
Pages: 229
PDF File Size: 8.43 Mb
ePub File Size: 14.88 Mb
ISBN: 872-4-36569-479-3
Downloads: 2968
Price: Free* [*Free Regsitration Required]
Uploader: Zulkisho

Sorption isotherms for oat flakes Avena sativa L. These curves were modeled using six equations adsorion applied in food. The quality of the fit was assessed with the regression coefficient r 2 and the mean relative percentage error MRPE. The best fit were obtained with the Caurie model with r 2 of 0. The equilibrium moisture presented a dependence on temperature in the studied a w range, as did the security moisture X S.

These results suggest that the recommended storage conditions of oat flakes include: Oat Avena sativa L. Compared with other cereals, oat is considered a source of proteins, carbohydrates, fiber, vitamins and minerals Gates, It has components of minor proportion, such as unsaturated fat and b -glucans, which contribute to the health and well-being of human beings Peterson, Oat flakes are an important raw material in the food industry Gates, One of the most important aspects concerning oat quality is its moisture content, since many of its physical properties depend on this property Prieto et al.

But its water activity a w is much more important, which indicates the water quantity in a food that adworcion be used for developmental biochemical reactions i. Predicting the variation of the equilibrium moisture content in solid materials, based on fundamentals principles, has not yet been developed for complex systems such as food matrices Al-Muhtaseb et al.

A common practice is to correlate the experimental data through mathematical models, which render adsorcikn results in certain a w ranges and certain food types Zhang et al.

Agronomía Colombiana

This adjustment is obtained by graphing the experimental moisture data in the product equilibrium at a pressure and temperature Corzo and Fuentes, with the thermodynamic addsorcion of water. The water activity in equilibrium equals the relative moisture adsorcuon the air that surrounds it Zhang et al. The most used strategy for studies on sorption desorption phenomena is sorption isotherms, which are important in the analysis and design of isoyermas food processes osotermas can be used to predict changes in food stability and to select appropriate packaging materials and ingredients Zhang et al.

The sorption-desorption behavior, as well as the isosteric heat of food products and the influence of temperature over the moisture content in equilibrium, provides very useful information for the processes of drying, preservation and conditioning of the food materials Badui, Besides, it defines the storing conditions that guarantee food stability Correa et al. Models that are available in the literature for describing moisture sorption isotherms can be divided into several categories: The GAB model is considered to be the most versatile sorption model available in the literature Al-Muhtaseb et al.

  GRAHAM WALLAS THE ART OF THOUGHT PDF

The Smith model Smith, is ieotermas in describing the sorption isotherm of biological materials such as starch and cellulose. Henderson proposed a semi-empirical model for the equilibrium moisture content of cereal grains.

In more recent years, the GAB d equation has been widely used to describe the sorption behavior of foods Adaorcion, ; Weisser, ; Iglesias et al. Having a reasonably small number of parameters threethe GAB equation has been found to adequately adsoorcion the experimental data in the range of water activity of the most practical interest in foods, i.

This model has been used with protein, rice, turkey, chicken, tomato, potato starch, and wheat starch Timmermann, On the other hand, the Oswin model has been used with meat and fruits Boquet et al. The purpose of this study was to experimentally determine the equilibrium moisture curves of oat flakes Avena sativa L.

Furthermore, the present study aimed to establish the best storage and packaging conditions for oat flakes. The oat product Avena sativa or A. From then on, the weight of the sample was controlled every 10 d until it achieved a constant weight equilibrium condition. Before doing the equilibrium moisture trials, the initial moisture of the oat flakes was determined by triplicate, following the methods of the AOAC No.

The equilibrium moisture content on a dry basis was plotted against the izotermas wto obtain the equilibrium idotermas curves. The quality isoteermas the fit of the proposed models was assessed with a linear correlation coefficient r 2 and the percentage of the mean relative error MRPE Eq. The r 2 must be higher than 0. The oat flake sample initial moisture was 0. This behavior can isoternas explained by the endothermic dissolution of sugars at raised values of a w Brett et al.

This fact was attributed to the higher energy levels and lower stability of water molecules as temperature increases, promoting their separation from the binding sites within the food matrix Breett et al. Under such conditions, the molecules in the glass stage may approximate to the glass transition region and become plasticized, thereby increasing their mobility and availability for sorption Brett et al.

Isotermas de adsorción de Langmuir para diferentes soluciones orgánicas de colesterol

The role of the glass transition in starch-rich products and how it affects their sorption mechanism has been studied by Al-Muhtaseb et al. The results obtained in this study confirm the premise of Van den Berg in relation to the modification of the sorption capacity around the transition region where the amorphous region of starch begins to be plasticized, increasing their availability of hydroxyl groups for the sorption of water molecules Brett et al.

On the other hand, starch, quantitatively the main component of cereals such as oat, contains two polymers that contribute to its molecular structure: Both molecules form semicrystalline superstructures with crystalline and amorphous layers arranged in an onion-like structure where most of the crystalline regions are formed by amylopectin although part of the amylose molecules are also present in them Zobel, ; Brett et al. Within such a system, amorphous zones are more water-accessible than crystalline regions in which the intermolecular interactions between the chains are too strong to allow solvent penetration.

Consequently, water influences the structure by acting as a plasticizer of the amorphous regions Al-Muhtaseb et al.

  DIN 0833-2 PDF

This effect causes adsrcion depression of the glass transition temperature Tg. The plasticizing effect is very small at low a w values; therefore, the Tg associated with the amorphous regions in samples will be typically high and the material will be glassy at room temperature.

Increasing water activity causes an increase in the availability of the adsorciin sites to the water molecules Al-Muhtaseb et al. Table 4 presents a summary of the results obtained for the proposed models with their respective constants and r 2 and MRPE values.

The Henderson model also presented a good behavior in respect to the r 2 but produced a high MRPE superior to This result does not agree with Brett et al. In this study, X S values equal to 0. Here, one can see that the curve predicted by the Caurie model is the best fit to the experimental data, consistent with those predicted by the r 2 and MRPE. Additionally, based on the results from Fig. The oat flake moisture sorption isotherms showed a clear dependence on temperature for the working values in this study.

The recommended storage conditions of oat flakes include: Analysis of starch and other main constituents of cereal grains.

Water sorption isotherms of starch powders. Official methods of analysis. Water sorption characteristics of six rowbarley malt Hordeum vulgare.

Isotermas de Adsorción by Arlette Huerta on Prezi

Using the GAB model to adsorciom sorption isotherms. Physical properties for foods. Applied Science Publishers, London. Equations for fitting water sorption isotherms of foods: Evaluation of various two-parameter models.

Moisture sorption characteristics of starchy products: Water adsorption isotherms of texturized soy protein. Da Silva, and L. Moisture sorption isotherms and modeling for precooked flours of pigeon pea Cajanus cajans L. Moisture sorption studies on onion powder. The prediction of moisture sorption isotherm adssorcion dairy powder.

Role of heat treatment in the processing and quality of oat flakes. University of Helsinki, Helsinki. An alternative to the GAB model for the mathematical description of moisture sorption isotherms of foods.

Water sorption isotherms in sugar beet root. Moisture sorption isotherm characteristics of plantain Musa AAB. Equilibrium moisture content and heat of desorption of some vegetables. Effect of temperature on the moisture sorption isotherm and water activity shift of two dehydrated food. Dyna 76 Glass transition temperatures and water sorption isotherms of cassava starch.

Oat a multifunctional grain. Isotemras Research Reports Agrifood Research, Jokioinen, Finland. Thermodynamics properties of food in dehydration. Engineering properties of foods.

Marcel Dekker, Adsorccion York. Effect of temperature on the water adsorption isotherms of sultana raisins. The sorption of water vapour by hight polymers.

A BET-like three sorption stage isotherm. Water sorption isotherms of foods and foods adsorvion Grain sorption equilibrium of quinoa grains. Van den Berg, C. Vapour sorption equilibrium and other water-starch interactions: Influence of temperature on sorption equilibrium. Properties of water in foods in relation to quality and stability. Desorption isotherms of some vegetables.